Cermet powder

ABSTRACT

A powder material of the present invention contains ceramic-metal composite particles, wherein at least a part of the composite particles exhibit no breaking point in a stress-strain diagram obtained by applying a compressive load that increases up to a maximum value of 10 mN or more at a loading rate of 15.0 mN/s or less.

TECHNICAL FIELD

The present invention relates to a cermet powder material includingceramic-metal composite particles.

BACKGROUND ART

Cermet particles, which are ceramic-metal composite particles, areutilized for various purposes, for example, used as a material forforming a thermal spray coating, namely, a thermal spray powder, asdescribed in Patent Document 1. One performance required for a thermalspray powder is that most of the powder thermally sprayed toward asubstrate adheres or deposits on the substrate to form a coating,namely, high deposit efficiency. Cermet particles, however, aregenerally difficult to thermally spray with high deposit efficiency, ascompared with metal particles. This is particularly remarkable in thecase of a low-temperature thermal spraying process, such as coldspraying, because the degree of melting and softening of the metalcomponent is reduced.

PRIOR ART DOCUMENTS

-   Patent Document 1: Japanese Laid-Open Patent Publication No.    2012-12686

SUMMARY OF THE INVENTION Problems that the Invention is to Solve

Accordingly, an objective of the present invention is to provide acermet powder material that is improved in terms of deposit efficiencywhen used as a thermal spray powder.

Means for Solving the Problems

In order to achieve the above objective and in accordance with oneaspect of the present invention, a powder material is provided thatincludes ceramic-metal composite particles, wherein at least a part ofthe composite particles exhibit no breaking point in a stress-straindiagram that is obtained by applying a compressive load that increasesup to a maximum value of 10 mN or more at a loading rate of 15.0 mN/s orless.

In accordance with another aspect of the present invention, a method forforming a thermal spray coating is provided that includes thermallyspraying the powder material according to the above aspect at a thermalspraying temperature of 3,000° C. or lower.

Effects of the Invention

The present invention succeeds in providing a cermet powder materialthat is improved in terms of deposit efficiency when used as a thermalspray powder.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a stress-strain diagram of two granulated-sintered cermetparticles exhibiting different stress-strain behaviors from each other.

FIGS. 2( a) and 2(b) are photographs of the cross section of agranulated-sintered cermet particle in a powder material of Example 2.

FIGS. 3( a) and 3(b) are photographs of the cross section of agranulated-sintered cermet particle in a powder material of ComparativeExample 2.

MODES FOR CARRYING OUT THE INVENTION

One embodiment of the present invention will now be described. Thepresent invention is not limited to the embodiment described below andappropriate modifications in design may be made to such an extent thatthe content of the present invention is not impaired.

A powder material according to the present embodiment is composed ofgranulated-sintered cermet particles. The granulated-sintered cermetparticles are a composite material of ceramic fine particles and metalfine particles, and are produced by sintering a granulated material(granule) obtained by granulating a mixture of the ceramic fineparticles and the metal fine particles.

The powder material of the present embodiment is used, for example, as athermal spray powder. That is, the powder material is used, for example,in an application in which the powder material is thermally sprayedtoward a substrate to thereby form a thermal spray coating on thesubstrate.

In order to obtain high deposit efficiency in use of the powder materialof the present embodiment as a thermal spray powder, it is necessarythat at least a part of the granulated-sintered cermet particles exhibitno breaking point in a stress-strain diagram that is obtained byapplying a compressive load that increases up to a maximum value of 10mN or more, preferably 100 mN or more, more preferably 200 mN or more,further preferably 500 mN or more, and most preferably 900 mN or more ata loading rate of 15.0 mN/s or less, preferably 14.0 mN/s or less, andmost preferably 13.0 mN/s or less.

A loading rate of 15.0 mN/s or less is a rate sufficient for deformingthe granulated-sintered cermet particle. As the loading rate when acompressive load is applied to the granulated-sintered cermet particleis lower, the disintegration properties of the granulated-sinteredcermet particle during a thermal spraying process can be more accuratelyevaluated.

A compressive load of 10 mN or more is a load sufficient for deformingthe granulated-sintered cermet particle. The compressive load applied tothe granulated-sintered cermet particle is preferably larger because thedisintegration properties of the granulated-sintered cermet particleduring a thermal spraying process can be more accurately evaluated.

The disintegration properties of the granulated-sintered cermet particlemean the ease of disintegration of the granulated-sintered cermetparticle, the behavior after disintegration, and others. The evaluationand control of disintegration properties of the granulated-sinteredcermet particle can lead to the amelioration of the problem of spitting(which is a phenomenon where a deposit made by adhesion or deposition ofa thermal spray powder excessively molten to the inner wall of a nozzlein a thermal spraying machine drops off the inner wall during thermalspraying of the thermal spray powder and is incorporated into a thermalspray coating, the phenomenon causing the reduction in performance ofthe thermal spray coating) and the problem of the reduction in hardnessof a thermal spray coating.

FIG. 1 is a stress-strain diagram that is obtained by applying acompressive load that increases up to a maximum value of 10 mN or moreat a loading rate of 15.0 mN/s or less, to two granulated-sinteredcermet particles exhibiting different stress-strain behaviors from eachother. In FIG. 1, while a line with symbol A shows the behavior with abreaking point where a strain rapidly increases at a certain stress, aline with symbol B shows the behavior without such a breaking point. Theproportion of granulated-sintered cermet particles exhibiting thestress-strain behavior shown by the line with symbol B in FIG. 1 to thegranulated-sintered cermet particles in the powder material of thepresent embodiment is preferably 1% or more, more preferably 5% or more,and further preferably 10% or more. All or almost all (for example,about 90%) of the granulated-sintered cermet particles may exhibit thestress-strain behavior shown by the line with symbol B in FIG. 1.

The proportion of granulated-sintered cermet particles exhibiting nobreaking point can be determined as follows, for example. That is, withrespect to granulated-sintered cermet particles arbitrarily selectedfrom the powder material and each having a predetermined particlediameter or less, the stress-strain behavior by applying a compressiveload that increases up to a maximum value of 10 mN or more at a loadingrate of 15.0 mN/s or less is measured. Then, the proportion ofgranulated-sintered cermet particles exhibiting no breaking point to thegranulated-sintered cermet particles tested is calculated. For example,a microcompression testing machine (MCTE-500, manufactured by ShimadzuCorporation) can be employed in the stress-strain behavior measurement,but not limited thereto.

A granulated-sintered cermet particle exhibiting the stress-strainbehavior shown by the line with symbol A in FIG. 1, when thermallysprayed toward a substrate, may cause breaking in collision with thesubstrate, and the resulting broken piece may rebound without depositingonto the substrate. On the contrary, a granulated-sintered cermetparticle exhibiting the stress-strain behavior shown by the line withsymbol B in FIG. 1 is likely to be plastically deformed without beingbroken in collision with the substrate, to deposit onto the substrate.As illustrated in FIG. 9 in Japanese Laid-Open Patent Publication No.2011-208165 that discloses a metal material for thermal spraying, ametal particle generally exhibits a stress-strain behavior having nobreaking point, and the stress-strain behavior shown by the line withsymbol B in FIG. 1 can be said to be similar therewith. It is consideredthat this is the reason why the powder material of the presentembodiment achieves high deposit efficiency when used as a thermal spraypowder, regardless of being composed of the cermet particles.

As a means for obtaining the granulated-sintered cermet particlesexhibiting no breaking point, it is effective to make the size of metalparticle portions in each granulated-sintered cermet particle small asmuch as possible.

Specifically, the average diameter (directed average diameter) of themetal particle portions is preferably 3 μm or less, more preferably 1 μmor less, further preferably 0.5 μm or less, and particularly preferably0.1 μm or less.

While the metal particle portions in each granulated-sintered cermetparticle serve as a binder that binds ceramic particle portions in thesame granulated-sintered cermet particle, application of a compressiveload to the granulated-sintered cermet particle may cause cracking onthe binding site between the ceramic particle portions to thereby breakthe granulated-sintered cermet particle. In this regard, as the averagediameter of the metal particle portions is smaller, the size of thebinding site between the ceramic particle portions is smaller, and as aresult, breaking of the granulated-sintered cermet particle caused bycracking on the binding site can be suppressed.

As another means for obtaining the granulated-sintered cermet particlesexhibiting no breaking point, it is also effective to make the size ofmetal particle portions in each granulated-sintered cermet particlesmaller than the size of ceramic particle portions in the samegranulated-sintered cermet particle. Specifically, the ratio of theaverage diameter (directed average diameter) of the metal particleportions to the average diameter (directed average diameter) of theceramic particle portions is preferably less than 1.5, more preferably 1or less, further preferably 0.5 or less, and most preferably 0.1 orless. As this ratio is smaller, the size of the binding site between theceramic particle portions is relatively smaller, and as a result,breaking of the granulated-sintered cermet particle caused by crackingon the binding site can be suppressed.

The average diameter (directed average diameter) of the ceramic particleportions in each granulated-sintered cermet particle is preferably 6 μmor less, more preferably 1 μm or less, further preferably 0.5 μm orless, and particularly preferably 0.1 μm or less.

As still another means for obtaining the granulated-sintered cermetparticles exhibiting no breaking point, it is also effective to make theratio of the average diameter (directed average diameter) of the metalparticle portions to the average diameter (volume average diameter) ofthe granulated-sintered cermet particles small as much as possible.Specifically, this ratio is preferably 0.15 or less, more preferably 0.1or less, further preferably 0.05 or less, and particularly preferably0.01 or less. As this ratio is smaller, the size of the binding sitebetween the ceramic particle portions is relatively smaller, and as aresult, breaking of the granulated-sintered cermet particle caused bycracking on the binding site can be suppressed.

The average diameter of the metal particle portions and the averagediameter of the ceramic particle portions in each granulated-sinteredcermet particle basically reflect the average diameter of the metal fineparticles and the average diameter of the ceramic fine particles,respectively, these fine particles being used in production of thegranulated-sintered cermet particles. These average diameters, however,are also affected by sintering that is performed in production of thegranulated-sintered cermet particles, and thus are generally slightlydifferent from the average diameter of the metal fine particles and theaverage diameter of the ceramic fine particles.

The ceramic fine particles for use in production of thegranulated-sintered cermet particles are composed of a single-componentceramic or a composite ceramic, for example, including at least oneselected from carbides, such as tungsten carbide and chromium carbide,borides, such as molybdenum boride and chromium boride, nitrides, suchas aluminum nitride, silicides, and oxides.

The metal fine particles for use in production of thegranulated-sintered cermet particles are composed of a single-componentmetal or a metal alloy, for example, including at least one selectedfrom cobalt, nickel, iron, chromium, silicon, aluminum, copper, andsilver. The metal fine particles are, however, preferably composed of ametal having a face-centered cubic lattice structure or a body-centeredcubic lattice structure. A metal having a face-centered cubic latticestructure or a body-centered cubic lattice structure is easilyslip-deformed, and thus a granulated-sintered cermet particle producedfrom such a metal is less likely to be broken when a compressive load isapplied. Specific examples of a metal having a face-centered cubiclattice structure include nickel, aluminum, and iron (y-iron) with anaustenite phase. Specific examples of a metal having a body-centeredcubic lattice structure include tungsten, molybdenum, and iron (α-iron)with a ferrite phase.

In particular, tungsten carbide fine particles and cobalt fine particlesare preferably used in combination. Since tungsten carbide and cobaltare highly wettable with each other, namely, compatible with each other,a granulated-sintered cermet particle produced by combining tungstencarbide fine particles and cobalt fine particles is less likely to bebroken when a compressive load is applied.

The metal particle portions are preferably present with being dispersedin each granulated-sintered cermet particle as much as possible. As ameans for allowing the metal particle portions to be present with beingdispersed, it is effective to sufficiently mix the ceramic fineparticles with the metal fine particles by a dry method or a wet method,preferably by a wet method, in production of the granulated-sinteredcermet particles.

The ceramic content in the granulated-sintered cermet particles ispreferably 95% by mass or less, more preferably 92% by mass or less, andfurther preferably 90% by mass or less. In other words, the metalcontent in the granulated-sintered cermet particles is preferably 5% bymass or more, more preferably 8% by mass or more, and further preferably10% by mass or more. As the ceramic content is lower (in other words, asthe metal content is higher), the plastic deformability of eachgranulated-sintered cermet particle is enhanced, and as a result, thepowder material is enhanced in terms of deposit efficiency when used asa thermal spray powder.

Each of the granulated-sintered cermet particles preferably has an outershape close to a true sphere as much as possible. Specifically, thegranulated-sintered cermet particles have an aspect ratio of preferably1.30 or less. A granulated-sintered cermet particle having an aspectratio of 1.30 or less is less likely to be broken when a compressiveload is applied. The aspect ratio of the granulated-sintered cermetparticle can be determined by, for example, dividing the length of thelong side of the minimum rectangle circumscribed to the particle as animage by a scanning electron microscope, by the length of the short sideof the same rectangle.

The granulated-sintered cermet particles each include pores having amedian diameter of preferably 2.0 μm or less, more preferably 1.7 μm orless, and further preferably 1.5 μm or less. When a compressive load isapplied to the granulated-sintered cermet particle, cracking may occuraround the pores in the granulated-sintered cermet particle to therebyallow the granulated-sintered cermet particle to be broken. In thisregard, as the median diameter of the pores is smaller, breaking of thegranulated-sintered cermet particle due to the occurrence of crackingaround the pores in the granulated-sintered cermet particle can besuppressed. The median diameter of the granulated-sintered cermetparticles, however, is preferably 0.001 μm or more, more preferably0.005 μm or more, and further preferably 0.01 μm or more from theviewpoint of the ease of coating formation.

The granulated-sintered cermet particles have a porosity of preferably30% or less, more preferably 25% or less, and further preferably 20% orless. As the porosity of the granulated-sintered cermet particles islower, breaking of each granulated-sintered cermet particle due to theoccurrence of cracking around the pores in the granulated-sinteredcermet particle can be suppressed. The porosity of thegranulated-sintered cermet particles, however, is preferably 0.1% ormore and further preferably 1% or more from the viewpoint of the ease ofcoating formation. The porosity of the granulated-sintered cermetparticles can be measured by, for example, a mercury intrusion method.

The above embodiment can be modified as follows.

-   -   The powder material of the above embodiment may include any        component other than the granulated-sintered cermet particles.        For example, the powder material may include free ceramic        particles or free metal particles. Alternatively, the powder        material may include molten-crushed cermet particles or        sintered-crushed cermet particles. The molten-crushed cermet        particles are produced by melting a mixture of ceramic fine        particles and metal fine particles, cooling and solidifying the        mixture molten, then crushing the mixture solidified, and then,        if necessary, classifying the mixture crushed. The        sintered-crushed cermet particles are produced by sintering and        crushing a mixture of ceramic fine particles and metal fine        particles, and then, if necessary, classifying the mixture        crushed.    -   The powder material of the above embodiment may be composed of        molten-crushed cermet particles or sintered-crushed cermet        particles instead of the granulated-sintered cermet particles,        or may include any component in addition to the molten-crushed        cermet particles or sintered-crushed cermet particles. A        granulated-sintered cermet particle, however, generally has an        outer shape close to a true sphere, as compared with a        molten-pulverized cermet particle and a sintered-pulverized        cermet particle, and is less likely to be broken when a        compressive load is applied. Also from the viewpoint that the        size and number of the pores can be arbitrarily controlled in a        relatively easy manner, the granulated-sintered cermet particles        are preferable.    -   When the powder material of the above embodiment is used as a        thermal spray powder, the powder material may be mixed with        other component and then thermally sprayed, or may be thermally        sprayed as it is without being mixed with other component.    -   The use of the powder material of the embodiment is not        particularly limited to a thermal spray powder, and the powder        material may be used as a material for forming a sintered body        or as polishing abrasives, for example. The powder material of        the above embodiment, however, includes granulated-sintered        cermet particles that are less likely to be broken when a        compressive load is applied, and thus the powder material is        suitable for an application in which a compressive load acts on        the powder material during use.    -   The thermal spraying temperature in the thermal spraying process        in which the powder material of the embodiment is thermally        sprayed is not particularly limited, but is preferably 3,000° C.        or lower, more preferably 2,500° C. or lower, and further        preferably 2,000° C. or lower in order to restrain spitting due        to excessive melting of the powder material or in order to        suppress thermal degradation of the ceramic fine particles in        the granulated-sintered cermet particles.    -   In addition, the thermal spraying temperature in the thermal        spraying process in which the powder material of the embodiment        is thermally sprayed is not particularly limited, but is        preferably 300° C. or higher, more preferably 400° C. or higher,        and further preferably 500° C. or higher in order to obtain high        deposit efficiency.    -   The method for thermally spraying the powder material of the        embodiment may be high velocity flame spraying, such as high        velocity oxygen fuel (HVOF) spraying, or may be explosion        thermal spraying or atmospheric plasma spraying (APS).        Alternatively, the method may also be a low-temperature thermal        spraying process, such as cold spraying, warm spraying, and high        velocity air fuel (HVAF) spraying. In cold spraying, a working        gas at a temperature lower than the melting point and the        softening point of the powder material is accelerated to a        supersonic velocity, and the working gas accelerated is used to        allow the powder material to collide and deposit onto a        substrate in the solid state. In warm spraying, a nitrogen gas        as a cooling gas is incorporated into a combustion flame in        which kerosene and oxygen as a combustion improver are used,        thereby forming a combustion flame at a lower temperature than        that of HVOF spraying, and this combustion flame heats and        accelerates the powder material to allow the powder material to        collide and deposit onto a substrate at a supersonic velocity.        In HVAF spraying, air is employed as a combustion improver        instead of oxygen to thereby form a combustion flame at a lower        temperature than that of HVOF spraying, and this combustion        flame heats and accelerates the powder material to allow the        powder material to collide and deposit onto a substrate.

Next, the present invention will be described more specifically withreference to examples and comparative examples.

Examples 1 to 7 and Comparative Examples 1 to 4 HVOF Spraying

Powder materials of Examples 1 to 7 and Comparative Examples 1 to 4,each of which is composed of granulated-sintered cermet particles, wereprepared, and were each thermally sprayed in conditions shown inTable 1. The details of each of the powder materials are shown in Table2. Although not shown in Table 2, the average diameter of thegranulated-sintered cermet particles in each of the powder materials wasmeasured using a laser diffraction/scattering particle size measuringapparatus “LA-300”, manufactured by Horiba Ltd., and all the averagediameters were found to be 17 μm.

The chemical composition of the granulated-sintered cermet particles ofeach of the powder materials is shown in the column “Composition ofcermet particles” in Table 2. In this column, “WC/12% Co” represents acermet including 12% by mass of cobalt and the balance of tungstencarbide, “WC/12% FeCrNi” represents a cermet including 12% by mass of aniron-chromium-nickel alloy and the balance of tungsten carbide, “WC/10%Co/4% Cr” represents a cermet including 10% by mass of cobalt, 4% bymass of chromium, and the balance of tungsten carbide, and “WC/20%CrC/7% Ni” represents a cermet including 20% by mass of chromiumcarbide, 7% by mass of nickel, and the balance of tungsten carbide. Thechemical composition of the granulated-sintered cermet particles wasmeasured using a fluorescent X-ray analysis apparatus “LAB CENTERXRF-1700”, manufactured by Shimadzu Corporation.

The measurement results of the respective average diameters (directedaverage diameters) of the ceramic particle portions and the metalparticle portions in the granulated-sintered cermet particles of each ofthe powder materials are shown in the columns “Average diameter ofceramic particle portions” and “Average diameter of metal particleportions” in Table 2, respectively. In this measurement, a scanningelectron microscope “S-3000N”, manufactured by Hitachi High-TechnologiesCorporation, was used. Specifically, the average diameter of the ceramicparticle portions and the average diameter of the metal particleportions were determined by observing the cross section of each of sixgranulated-sintered cermet particles having a particle diameter within±3 μm from the average diameter of the granulated-sintered cermetparticles by a reflection electron microscope at 5,000-foldmagnification, and using the resulting cross section photograph of eachof the particles. For reference, the cross section photographs of thegranulated-sintered cermet particles of the powder materials in Example2 and Comparative Example 2 are shown in FIGS. 2 and 3, respectively.

The value obtained by dividing the average diameter of the metalparticle portions by the average diameter of the ceramic particleportions, the average diameters being determined as above with respectto each of the powder materials, is shown in the column “Averagediameter of metal particle portions/Average diameter of ceramic particleportions” in Table 2.

The measurement result of the median diameter of pores in thegranulated-sintered particles of each of the powder materials is shownin the column “Median diameter of pores” in Table 2. More specifically,the median diameter of the pores was determined by performing ameasurement using a mercury intrusion porosimeter “AutoPore IV 9500”,manufactured by Micromeritics, in conditions of a mercury contact angleof 130° and a surface tension of 485 dynes/cm (0.485 N/m), andextracting data of 66 psi (0.045 MPa) or more from the measurementresults.

The result obtained by measuring the proportion of granulated-sinteredcermet particles exhibiting no breaking point in a stress-strain diagramthat was obtained by applying a compressive load that increased up to amaximum value of 981 mN at a loading rate of 12.9 mN/s, to thegranulated-sintered cermet particles of each of the powder materials,using a microcompression testing machine (MCTE-500, manufactured byShimadzu Corporation) is shown in the column “Proportion of cermetparticles exhibiting no breaking point” in Table 2. The proportion ofthe granulated-sintered cermet particles exhibiting no breaking pointwas calculated as a proportion of granulated-sintered cermet particlesexhibiting no breaking point in 12 granulated-sintered cermet particleshaving a particle diameter of 50 μm or less arbitrarily selected in eachof the powder materials.

The process temperature in thermal spraying of each of the powdermaterials in conditions shown in Table 1 is shown in the column “Thermalspraying temperature” in Table 2.

The value obtained by dividing the weight of a thermal spray coatingobtained by thermal spraying of each of the powder materials by theweight of the powder material thermally sprayed is shown on percentagebasis in the column “Deposit efficiency” in Table 2.

TABLE 1 Thermal spraying machine: HVOF spraying machine “JP-5000”,manufactured by Praxair/TAFA Inc. Flow rate of oxygen: 1,900 scfh (about893 L/min) Flow rate of kerosene: 5.1 gph (about 0.32 L/min) Thermalspraying distance: 380 mm Barrel length of thermal spraying machine: 4inches (about 101.6 mm) Substrate: SS 400 plate blast-treated

TABLE 2 Average Average diameter of Proportion of diameter of Averagemetal particle cermet particles Thermal Composition ceramic diameter ofportions/Average Median exhibiting no spraying Deposit of cermetparticle metal particle diameter of ceramic diameter of breakingtemperature efficiency particles portions (μm) portions (μm) particleportions pores (μm) point (%) (° C.) (%) Example 1 WC/12% Co 2 0.7 0.350.3 25% 1900 49 Example 2 WC/12% Co 0.2 0.14 0.7 0.3 25% 1900 55 Example3 WC/12% Co 2 0.7 0.35 0.3 13% 1900 48 Example 4 WC/12% Co 2 0.7 0.350.3 87% 1900 59 Example 5 WC/10% Co/4% Cr 2 0.7 0.35 0.3 13% 1900 47Example 6 WC/20% CrC/7% Ni 2 0.7 0.35 0.3 13% 1900 47 Example 7 WC/12%FeCrNi 2 0.7 0.35 0.3 13% 1900 51 Comparative WC/12% Co 2 3 1.5 0.3  0%1900 44 Example 1 Comparative WC/12% Co 0.7 3 4.3 0.01>  0% 1900 45Example 2 Comparative WC/12% Co 2 3 1.5 0.01>  0% 1900 37 Example 3Comparative WC/12% Co 2 3 1.5 2.5  0% 1900 33 Example 4

As shown in Table 2, in the case where each of the powder materials ofExamples 1 to 7 was used, high deposit efficiency could be obtained ascompared with the case where each of the powder materials of ComparativeExamples 1 to 4 was used.

Examples 8 to 11 and Comparative Examples 5 to 7 Cold Spraying

Powder materials of Examples 8 to 11 and Comparative Examples 5 to 7,each of which is composed of granulated-sintered cermet particles, wereprepared, and were each thermally sprayed in conditions shown in Table3. The details of each of the powder materials are shown in Table 4.Although not shown in Table 4, the average diameter of thegranulated-sintered cermet particle in each of the powder materials wasmeasured using a laser diffraction/scattering particle size measuringapparatus “LA-300”, manufactured by Horiba Ltd., and all the averagediameters were found to be 17 μm.

The chemical composition of the granulated-sintered cermet particle ofeach of the powder materials is shown in the column “Composition ofcermet particle” in Table 4. In this column, “WC/25% FeCrNi” representsa cermet including 25% by mass of an iron-chromium-nickel alloy and thebalance of tungsten carbide, and WC/25% FeSiCr” represents a cermetincluding 25% by mass of an iron-silicon-chromium alloy and the balanceof tungsten carbide. The chemical composition of the granulated-sinteredcermet particle was measured using a fluorescent X-ray analysisapparatus “LAB CENTER XRF-1700”, manufactured by Shimadzu Corporation.

The measurement results of the respective average diameters (directedaverage diameters) of the ceramic particle portions and the metalparticle portions in the granulated-sintered cermet particles of each ofthe powder materials are shown in the columns “Average diameter ofceramic particle portions” and “Average diameter of metal particleportions” in Table 4, respectively. In this measurement, a scanningelectron microscope “S-3000N”, manufactured by Hitachi High-TechnologiesCorporation, was used. Specifically, the average diameter of the ceramicparticle portions and the average diameter of the metal particleportions were determined by observing the cross section of each of sixgranulated-sintered cermet particles having a particle diameter within±3 μm from the average diameter of the granulated-sintered cermetparticles by a reflection electron microscope at 5,000-foldmagnification, and using the resulting cross section photograph of eachof the particles.

The value obtained by dividing the average diameter of the metalparticle portions by the average diameter of the ceramic particleportions, the average diameters being determined as above with respectto each of the powder materials, is shown in the column “Averagediameter of metal particle portions/Average diameter of ceramic particleportions” in Table 4.

The measurement result of the median diameter of pores in thegranulated-sintered particles of each of the powder materials is shownin the column “Median diameter of pores” in Table 4. More specifically,the median diameter of the pores was determined by performing ameasurement using a mercury intrusion porosimeter “AutoPore IV 9500”,manufactured by Micromeritics, in conditions of a mercury contact angleof 130° and a surface tension of 485 dynes/cm (0.485 N/m), andextracting data of 66 psi (0.045 MPa) or more from the measurementresults.

The result obtained by measuring the proportion of a granulated-sinteredcermet particles exhibiting no breaking point in a stress-strain diagramthat was obtained by applying a compressive load that increased up to amaximum value of 200 mN at a loading rate of 12.9 mN/s, to thegranulated-sintered cermet particle of each of the powder materials,using a microcompression testing machine (MCTE-500, manufactured byShimadzu Corporation) is shown in the column “Proportion of cermetparticles exhibiting no breaking point” in Table 4. The proportion ofthe granulated-sintered cermet particle exhibiting no breaking point wascalculated as a proportion of granulated-sintered cermet particleexhibiting no breaking point in 12 granulated-sintered cermet particleshaving a particle diameter of 30 μm or less arbitrarily selected in eachof the powder materials.

The process temperature in thermal spraying of each of the powdermaterials in conditions shown in Table 3 is shown in the column “Thermalspraying temperature” in Table 4.

The result obtained by evaluating the deposit efficiency of each of thepowder materials based on the thickness of a thermal spray coatingformed per passage of the thermal spraying nozzle in thermal spraying ofeach of the powder materials in conditions shown in Table 3 is shown inthe column “Deposit efficiency” in Table 4. Specifically, the case wherethe thickness of the thermal spray coating formed per passage was 200 μmor more was rated as “Good”, and the case where the thickness was lessthan 200 μm was rated as “Poor”.

TABLE 3 Thermal spraying machine: low pressure cold spraying apparatus“DYMET”, manufactured by OCPS Type of working gas: air Pressure ofworking gas: 0.7 MPa Temperature of working gas heater: 500° C. Thermalspraying distance: 20 mm Traverse velocity: 5 mm/sec. Amount of powdermaterial supplied: 15 g/min. Substrate: SS 400 plate blast-treated

TABLE 4 Average Average diameter of Proportion of diameter of Averagemetal particle cermet particles Thermal Composition ceramic diameter ofportions/Average Median exhibiting no spraying of cermet particle metalparticle diameter of ceramic diameter of breaking temperature Depositparticles portions (μm) portions (μm) particle portions pores (μm) point(%) (° C.) efficiency Example 8 WC/25% FeCrNi 2 0.7 0.35 0.3 87% 400Good Example 9 WC/25% FeCrNi 2 0.7 0.35 0.3 25% 400 Good Example 10WC/25% FeCrNi 2 0.7 0.35 0.3 13% 400 Good Comparative WC/25% FeCrNi 2 31.5 0.3  0% 400 Poor Example 5 Comparative WC/25% FeCrNi 0.7 3 4.3 0.01> 0% 400 Poor Example 6 Example 11 WC/25% FeSiCr 2 0.7 0.35 0.3 13% 400Good Comparative WC/25% FeSiCr 2 3 1.5 0.3  0% 400 Poor Example 7

As shown in Table 4, in the case where each of the powder materials ofExamples 8 to 11 was used, high deposit efficiency could be obtained ascompared with the case where each of the powder materials of ComparativeExamples 5 to 7 was used.

1. A powder material comprising ceramic-metal composite particles,wherein at least a part of the composite particles exhibit no breakingpoint in a stress-strain diagram that is obtained by applying acompressive load that increases up to a maximum value of 10 mN or moreat a loading rate of 15.0 mN/s or less.
 2. The powder material accordingto claim 1, wherein the composite particles have a proportion of thecomposite particles exhibiting no breaking point of 10% or more.
 3. Thepowder material according to claim 1, wherein the composite particleseach include metal particle portions having an average diameter of 3 μmor less.
 4. The powder material according to claim 1, wherein thecomposite particles each include metal particle portions and ceramicparticle portions and have a ratio of an average diameter of the metalparticle portions to an average diameter of the ceramic particleportions of less than 1.5.
 5. The powder material according to claim 1,wherein the composite particles each include metal particle portions andceramic particle portions and have a ratio of an average diameter of themetal particle portions to an average diameter of the ceramic particleportions of less than 1.5, and the average diameter of the metalparticle portions is 3 μm or less.
 6. The powder material according toclaim 1, wherein the composite particles each include metal particleportions, and a ratio of an average diameter of the metal particleportions to an average diameter of the composite particles is 0.15 orless.
 7. The powder material according to claim 1, wherein the compositeparticles have an aspect ratio of 1.30 or less.
 8. The powder materialaccording to claim 1, wherein the composite particles each include poreshaving a median diameter of 2.0 μm or less.
 9. The powder materialaccording to claim 1, wherein the composite particles have a porosity of30% or less.
 10. The powder material according to claim 1, wherein thepowder material is used as a thermal spray powder.
 11. The powdermaterial according to claim 10, wherein the powder material is thermallysprayed at a thermal spraying temperature of 3,000° C. or lower.
 12. Amethod for forming a thermal spray coating, comprising thermallyspraying the powder material according to claim 1 at a thermal sprayingtemperature of 3,000° C. or lower.
 13. The powder material according toclaim 1, wherein the at least a part of the composite particles exhibitno breaking point in a stress-strain diagram that is obtained byapplying a compressive load that increases up to a maximum value of 100mN or more at a loading rate of 15.0 mN/s or less.
 14. The powdermaterial according to claim 1, wherein the composite particles eachinclude ceramic particle portions containing at least one selected fromtungsten carbide, chromium carbide, molybdenum boride, chromium boride,and aluminum nitride.
 15. The powder material according to claim 1,wherein the composite particles each include metal particle portionshaving a face-centered cubic lattice structure or a body-centered cubiclattice structure.
 16. A powder material comprising ceramic-metalcomposite particles, wherein at least 10% of the composite particlesexhibit no breaking point in a stress-strain diagram that is obtained byapplying a compressive load that increases up to a maximum value of 200mN or more at a loading rate of 15.0 mN/s or less, the compositeparticles each include ceramic particle portions containing tungstencarbide and metal particle portions containing cobalt, nickel, iron, orchromium, the composite particles have a ratio of an average diameter ofthe metal particle portions to an average diameter of the ceramicparticle portions of less than 1, the average diameter of the metalparticle portions is 1 μm or less, a ratio of the average diameter ofthe metal particle portions to the average diameter of the compositeparticles is 0.1 or less, and the composite particles each include poreshaving a median diameter of 2.0 μm or less.